# 3 — Coder (coder) — main.py

**Malli:** `qwen-coder`

## System Prompt

```
You are an expert Python developer. Write complete, production-ready code.

CRITICAL RULES:
1. Include ALL imports at the top of every file
2. Import from other project files: from models import User, SessionLocal
3. Pydantic schemas use different names than SQLAlchemy models: UserCreate, UserResponse (not User)
4. SQLAlchemy engine: create_engine(url, connect_args={"check_same_thread": False})
5. SessionLocal: sessionmaker(autocommit=False, autoflush=False, bind=engine)
6. FastAPI dependencies: def get_db(): db = SessionLocal(); try: yield db; finally: db.close()
7. Pydantic v2: use model_dump() not dict(), class Config: from_attributes = True
8. All CRUD endpoints: POST (201), GET list, GET by id, PUT, DELETE (204)

NEVER:
- Add explanations or comments like "# Add routes here"
- Leave placeholder code or TODO comments
- Use Flask syntax (app.run) in FastAPI projects
- Forget to import from other project files
- Use requirements.txt or Poetry — always use pyproject.toml with [project] format (PEP 621)
- Use pip install — use uv (e.g. uv run uvicorn main:app --reload)
```

## Syöte

```
You are an expert Python developer. Write complete, production-ready code.

CRITICAL RULES:
1. Include ALL imports at the top of every file
2. Import from other project files: from models import User, SessionLocal
3. Pydantic schemas use different names than SQLAlchemy models: UserCreate, UserResponse (not User)
4. SQLAlchemy engine: create_engine(url, connect_args={"check_same_thread": False})
5. SessionLocal: sessionmaker(autocommit=False, autoflush=False, bind=engine)
6. FastAPI dependencies: def get_db(): db = SessionLocal(); try: yield db; finally: db.close()
7. Pydantic v2: use model_dump() not dict(), class Config: from_attributes = True
8. All CRUD endpoints: POST (201), GET list, GET by id, PUT, DELETE (204)

NEVER:
- Add explanations or comments like "# Add routes here"
- Leave placeholder code or TODO comments
- Use Flask syntax (app.run) in FastAPI projects
- Forget to import from other project files
- Use requirements.txt or Poetry — always use pyproject.toml with [project] format (PEP 621)
- Use pip install — use uv (e.g. uv run uvicorn main:app --reload)

EXAMPLE of main.py (for a different project, adapt to this one):
```
from fastapi import FastAPI, Depends, HTTPException
from sqlalchemy.orm import Session
from models import Base, engine, SessionLocal, Item
from schemas import ItemCreate, ItemResponse

Base.metadata.create_all(bind=engine)
app = FastAPI()

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

@app.post("/items/", response_model=ItemResponse, status_code=201)
def create_item(item: ItemCreate, db: Session = Depends(get_db)):
    db_item = Item(**item.model_dump())
    db.add(db_item)
    db.commit()
    db.refresh(db_item)
    return db_item

@app.get("/items/", response_model=list[ItemResponse])
def list_items(db: Session = Depends(get_db)):
    return db.query(Item).all()

@app.get("/items/{item_id}", response_model=ItemResponse)
def get_item(item_id: int, db: Session = Depends(get_db)):
    item = db.query(Item).filter(Item.id == item_id).first()
    if not item:
        raise HTTPException(status_code=404, detail="Not found")
    return item

@app.put("/items/{item_id}", response_model=ItemResponse)
def update_item(item_id: int, item: ItemCreate, db: Session = Depends(get_db)):
    db_item = db.query(Item).filter(Item.id == item_id).first()
    if not db_item:
        raise HTTPException(status_code=404, detail="Not found")
    for key, value in item.model_dump().items():
        setattr(db_item, key, value)
    db.commit()
    db.refresh(db_item)
    return db_item

@app.delete("/items/{item_id}", status_code=204)
def delete_item(item_id: int, db: Session = Depends(get_db)):
    db_item = db.query(Item).filter(Item.id == item_id).first()
    if not db_item:
        raise HTTPException(status_code=404, detail="Not found")
    db.delete(db_item)
    db.commit()
```

Already written files in THIS project:
--- models.py ---
from sqlalchemy import create_engine, Column, Integer, String, Date, Enum
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

DATABASE_URL = "sqlite:///./todo.db"
engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base()

class Todo(Base):
    __tablename__ = "todos"
    id = Column(Integer, primary_key=True, index=True)
    title = Column(String(100), nullable=False)
    description = Column(String(500))
    due_date = Column(Date, nullable=False)
    status = Column(Enum('pending', 'completed'), default='pending')

--- schemas.py ---
from pydantic import BaseModel

class TodoCreate(BaseModel):
    title: str
    description: str | None = None
    due_date: date
    status: str = 'pending'

class TodoResponse(TodoCreate):
    id: int

    class Config:
        from_attributes = True

PROJECT REQUIREMENTS (from product owner):
1. **PROJECT NAME:** Todo-sovellus

2. **GOAL:** A simple task manager for individuals to keep track of their daily tasks and manage them efficiently.

3. **CORE FEATURES:**
   - Create new todos with title, description, due date.
   - Read/View all todos or a single todo by ID.
   - Update existing todos (title, description, status).
   - Delete completed or unnecessary todos.
   - Filter todos by status (e.g., pending, completed).

4. **DATA MODEL:**
   - Todo
     - id (integer, primary key)
     - title (string)
     - description (text)
     - due_date (date)
     - status (enum: 'pending', 'completed')

5. **API ENDPOINTS:**
   - GET /todos: Retrieve all todos.
   - GET /todos/{id}: Retrieve a single todo by ID.
   - POST /todos: Create a new todo.
   - PUT /todos/{id}: Update an existing todo.
   - DELETE /todos/{id}: Delete a todo.

6. **CONSTRAINTS:**
   - Must use SQLite as the database.
   - No authentication required for accessing endpoints.
   - Implement unit tests and integration tests to ensure functionality.

NOW write "main.py" for THIS project: Todo-sovellus FastAPI + SQLite, CRUD-endpointit ja testit
Create the FastAPI app with all CRUD endpoints:
- Import from models.py and schemas.py (use exact class names)
- create_all(bind=engine) at module level
- get_db dependency with yield pattern
- POST (201), GET list, GET by id, PUT, DELETE (204)
- Use response_model for type safety
- Use model_dump() not dict() (Pydantic v2)
Adapt to the project requirements. Import from already written files. Write ONLY the code, no explanations.
```

## Tulos

```
from fastapi import FastAPI, Depends, HTTPException
from sqlalchemy.orm import Session
from models import Base, engine, SessionLocal, Todo
from schemas import TodoCreate, TodoResponse

Base.metadata.create_all(bind=engine)
app = FastAPI()

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

@app.post("/todos/", response_model=TodoResponse, status_code=201)
def create_todo(todo: TodoCreate, db: Session = Depends(get_db)):
    db_todo = Todo(**todo.model_dump())
    db.add(db_todo)
    db.commit()
    db.refresh(db_todo)
    return db_todo

@app.get("/todos/", response_model=list[TodoResponse])
def list_todos(status: str | None = None, db: Session = Depends(get_db)):
    if status:
        query = db.query(Todo).filter_by(status=status)
    else:
        query = db.query(Todo)
    return query.all()

@app.get("/todos/{todo_id}", response_model=TodoResponse)
def get_todo(todo_id: int, db: Session = Depends(get_db)):
    todo = db.query(Todo).filter(Todo.id == todo_id).first()
    if not todo:
        raise HTTPException(status_code=404, detail="Not found")
    return todo

@app.put("/todos/{todo_id}", response_model=TodoResponse)
def update_todo(todo_id: int, todo: TodoCreate, db: Session = Depends(get_db)):
    db_todo = db.query(Todo).filter(Todo.id == todo_id).first()
    if not db_todo:
        raise HTTPException(status_code=404, detail="Not found")
    for key, value in todo.model_dump().items():
        setattr(db_todo, key, value)
    db.commit()
    db.refresh(db_todo)
    return db_todo

@app.delete("/todos/{todo_id}", status_code=204)
def delete_todo(todo_id: int, db: Session = Depends(get_db)):
    db_todo = db.query(Todo).filter(Todo.id == todo_id).first()
    if not db_todo:
        raise HTTPException(status_code=404, detail="Not found")
    db.delete(db_todo)
    db.commit()
```